1. Field of the Invention
This invention relates to methods and compositions for the catalytic oxidation of gaseous carbonaceous emissions, in particular, gaseous carbonaceous emissions that include halogenated compounds.
2. Description of Related Art
The treatment of gaseous emissions containing volatile organic compounds has been of increasing concern in recent years. Thermal incineration, catalytic oxidation and adsorption are commonly used for removing these pollutants. Thermal incineration requires high operating temperatures and high capital cost facilities. If the gaseous stream also includes halogenated compounds, thermal incineration can evolve toxic halogenated compounds under certain operating conditions. In some instances, adsorption by adsorbents such as carbon is an alterative; however, this process does not destroy the pollutants, but merely concentrates them. Furthermore, adsorption efficiency can be adversely impacted by fluctuating concentrations of the gaseous components.
Catalytic oxidation is an energy efficient and economical way of destroying gaseous organic emissions. It operates at significantly lower temperatures and shorter residence time than thermal incineration and requires smaller reactors made of less expensive materials.
Methods for the catalytic oxidation of non-halogenated organic and halogenated organic compounds are well known in the art. For example, in the article by G. C. Bond and N. Sadeghi, "Catalyzed Destruction of Chlorinated Hydrocarbons" J. Appl. Chem. Biotechnol., 1975, 25, 241-248, it is reported that chlorinated hydrocarbons are converted to HCl and CO.sub.2 over platinum on gamma alumina catalysts.
U.S. Pat. Nos. 3,972,979 and 4,053,557 describe the decomposition of halogenated hydrocarbons by oxidation over chromium oxide or a boehmite supported platinum.
U.S. Pat. Nos. 4,059,675, 4,059,676 and 4,059,683 describe methods for decomposing halogenated organic compounds using catalysts containing ruthenium, ruthenium-platinum and platinum, respectively, in the presence of an oxidizing agent at a temperature of at least 350.degree. C.
The article by James J. Spivy, "Complete Catalytic Oxidation of Volatile Organics", Ind. Eng. Chem. Res., 1987, 26, 2165-2180, is a review of the literature dealing with the heterogenous catalytic oxidation of volatile organic compounds.
The article by S. Chatterjee and H. L. Green, "Oxidative Catalysis by Chlorinated Hydrocarbons by Metal-Load Acid Catalysts", Journal of Catalysis, 1991, 130, 76-85, reports on a study of the catalytic oxidation of methylene chloride in air using supported zeolite catalysts H-Y, Cr-Y, and Ce-Y.
PCT international application No. PCT/US 90/02386 describes a catalytic process for converting or destroying organic compounds including organohalogen compounds using a catalyst which contains as a catalytic component titania. The preferred catalyst also contains vanadium oxide, tungsten oxide, tin oxide, and at least one noble metal selected from the group consisting of platinum, palladium, and rhodium characterized in that the vanadium oxide, tungsten oxide and noble metals are uniformly dispersed on the titania.
U.S. Pat. No. 5,283,041 (commonly assigned to assignee of the instant invention), hereby incorporated by reference, discloses an oxidation catalyst for treating a gas stream containing compounds selected from the group consisting of halogenated organic compounds, other organic compounds and mixtures thereof; the catalyst comprising a core material comprising zirconium oxide and one or more oxides of manganese, cerium or cobalt with vanadium oxide and, preferably, platinum group metal dispersed on the core material.
U.S. Pat. No. 5,643,545 (commonly assigned to assignee of the instant invention), hereby incorporated by reference, relates to treatment of streams containing halogenated organic compounds and volatile organic compounds (VOCs) with catalytic materials deposited on high acidity and/or low acidity supports.
U.S. Pat. Nos. 5,578,283 and 5,653,949, (commonly assigned to assignee of the present invention), hereby incorporated by reference, relate to treatment of gases containing halogenated organic compounds, non-halogenated organic compounds, carbon monoxide or mixtures thereof. Catalyst compositions useful in the treatment comprise at least one platinum group metal, zirconium oxide and at least one oxide of manganese, cerium or cobalt. A further composition disclosed uses the foregoing described components but which is substantially free of vanadium in a process for treating a gas stream containing at least one brominated organic compound.
While the foregoing references describe methods and compositions for treatment of streams containing carbonaceous compounds and halogenated organic compounds, there is no recognition of any problems which arise during the treatment of emission streams particularly those containing halogenated organic compounds and non-halogenated organic compounds such as methane and benzene. For example, emissions from production of terephthalic acid typically contain carbon monoxide, methane, methyl bromide, and hydrocarbons such as benzene and toluene. It has been observed that as catalysts age, their catalytic effectiveness decreases and to compensate for this decreased effectiveness, process temperatures are raised to complete the desired catalysis. However, for the case of terephthalic acid production, the increased process temperatures unfavorably results in bromination of methane and bromination of benzene. For example, it has been found that benzene bromination occurs at temperatures as low as 300.degree. C. and that methane bromination occurs at temperatures low as 420.degree. C. using a platinum-based catalyst. The bromination of methane has a deleterious effect on the overall conversion of methyl bromide. Additionally, bromination of benzene gives rise to bromobenzene, dibromobenzene, and tetrabromobenzene. The deleterious effects of forming these brominated benzenes is that these compounds are formed in the solid phase which cause plugging or blockage in process lines.
The present invention provides a solution to the aforesaid problems by offering methods and catalytic compositions which oxidize non-halogenated and halogenated organic compounds while suppressing halogenation of other gas stream compounds such as methane and benzene with the oxidation products of the halogenated compounds.